1. Field of the Invention
The present invention relates to a MEMS device having a microphone structure, and to a method for the production thereof.
2. Description of the Related Art
The microphone structure is realized in a layer construction on a base substrate; it includes a deflectable microphone diaphragm and a stationary counter-element having ventilation openings. The microphone diaphragm spans a through-opening in the base substrate, the mid-region of the microphone diaphragm being essentially plane-parallel to the substrate plane and, in the rest state, being situated inside the through-opening in the base substrate. The microphone diaphragm is provided with at least one deflectable electrode of a microphone condenser system. The stationary counter-element is configured in a layer construction over the microphone diaphragm, and acts as bearer for at least one stationary electrode of the microphone condenser system.
Such a microphone device is described in US Patent Application Publication No. 2011/0311081 A1. Here, the microphone diaphragm is applied in the form of a metallic layer in the floor region of a recess in the surface of the base substrate. Subsequently, the counter-element is realized in a layer construction on the surface of the base substrate. As a consequence, the spacing between the microphone diaphragm and the counter-element is here essentially determined by the depth of the recess in the substrate surface. The metallic microphone diaphragm is bonded to the layer construction on the substrate surface via a dielectric coating on the side wall of the recess. The metallic microphone diaphragm, together with its dielectric suspension, is also exposed at the rear side only after the rear side etching process in which the through-opening in the base substrate is produced, so that the diaphragm spans this through-opening. Corresponding to the depth and shape of the recess in the substrate surface, the metallic mid-region of the microphone diaphragm is situated under the substrate surface and is oriented parallel to the substrate plane.
The device design described in US Patent Application Publication No. 2011/0311081 A1 enables the realization of micromechanical microphone structures having a relatively large gap spacing between the microphone diaphragm and counter-element, which has a positive effect on the microphone performance. Because here the microphone diaphragm is sunk into the substrate plane, this gap spacing can be achieved with a comparatively low constructive height of the device.
However, the known microphone device is also problematic in several ways.
Thus, the combination of the metallic diaphragm material with the dielectric material of the diaphragm suspension necessarily causes mechanical tensions in the diaphragm structure which have a disadvantageous effect on the microphone properties. Thus, for example the sensitivity of the microphone varies with temperature. Moreover, in the case of the known microphone device an acoustic seal of the microphone structure can be realized only through a circumferential bonding of the microphone diaphragm to the layer construction of the device. However, this works against the dismantling of mechanical tensions in the diaphragm structure. In addition, the known microphone device has only one electrical device as overload protection, which is intended to prevent an electrostatic adhesion of the microphone diaphragm to the counter-element. Here, an overload protection at the substrate side for the microphone diaphragm is not provided.